It is assumed that in the future, needs for color image formation employing electrophotographic image forming apparatuses, represented by laser printers and MFP (multifunctional peripherals), will increase further. In addition, to implement that further spread, down-sizing and easier maintenance are also sought. Mainly employed as color image forming apparatuses to meet the above needs are those which employ a non-magnetic single component developer (or called as a non-magnetic single component toner) capable of forming images without carriers. For example, mainly employed as an image forming method employing the non-magnetic single component developer is one in which a latent image formed on an electrostatic latent image carrying member is developed via a non-magnetic single component developer composed of toner which is conveyed and fed via a developer carrying member such as a development roller, and the formed toner image is transferred onto the transfer material, followed by thermal fixing of the toner image on the transfer material.
Further in recent years, the market demands rapid full-color image formation to produce handout materials for office conferences and POP advertisements. When printing is carried out employing a downsized high rate color printer, toner is demanded to exhibit rapid and consistent initial electrostatic charge increasing capability. As techniques to meet such needs, there is one which realizes rapid initial electrostatic charge increase employing a pulverized toner incorporating, for example, polyester resins, colorants, electrostatic charge controlling agents, and oxidation type polyolefin waxes (refer, for example, to Patent Document 1).
However, the toner disclosed in the above patent adversely affects production cost due to limitation of component materials. Further, the above toner is not always preferable since during continuous printing, the resulting image density tends to gradually decrease due to charge-up.
When the recent technical trend of toner is reviewed, so-called polymerization toners have increasingly been developed which are produced via a process in which resin particles are aggregated in an aqueous medium. The polymerization toner is suited for a production process in which small particles of uniform shape and particle size distribution are produced, whereby it is possible to provide optimal toner for formation of pictorial images (refer, for example, to Patent Document 2).
Further, downsizing image forming apparatuses is progressing. When an apparatus is downsized, impact applied to toner and constituting member tend to increase, whereby investigation to provide devices with higher durability has been conducted. For example, a toner production technique is disclosed which controls hardness of toner particles during particle formation in an aqueous medium (refer, for example, to Patent Document 3).
(Patent Document 1) Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 2000-235280
(Patent Document 2) JP-A No. 2000-214629
(Patent Document 3) JP-A No. 2000-347445